This invention relates in general to speaker phone operation in portable communication devices, and more particularly to the arbitration between the inbound and outbound audio paths in leaky network environments where inbound echo is present.
Portable communication devices such as cellular telephones have achieved widespread market distribution, and are commonly used by many people, particularly in metropolitan areas. Cellular phone technology is approaching maturity, and more frequently cellular phone manufactures are looking for features to add to cellular phones to increase their marketability and usefulness. One such feature is the speakerphone mode of operation.
Implementing a speakerphone in a cellular phone has long been a difficult challenge. There are several reasons for this. A significant reason is the environment where cellular phones are used varies greatly, unlike regular land-line speakerphone/phones which are more typically used in office or home environments. The places where cellular phones are used often have high amounts of background noise, and particularly fricative like sounds, such as the sound or air rushing over an automobile while the automobile is in motion. A variety of such problems have been addressed in U.S. Pat. Nos. 6,122,531, 6,138,040, and 6,157,902, all of which are assigned to the present assignee.
These three patents describe various problems involved in operating a simplex speakerphone, and the arbitration between the two audio paths in the presence of noisy backgrounds. However, it has been discovered that other factors affect the arbitration that are not due to external acoustic noise, but idiosyncrasies of the telephone communications systems. Specifically, it has been found that the voice energy of the user of the portable communication device being operated in a speakerphone mode can come back as echo from the infrastructure switching equipment. This echo, if received during a pause in the users speech, can cause the portable communication device to decide that incoming speech has been received and shut off the microphone path and activate the speaker path. When the user begins speaking again, if the echo is still present, the portable communication device will ignore the microphone path until after cessation of the echo. This causes an omission in the user""s speech to be heard by the far end party. It also causes the user to hear pops and crackling sounds while speaking. Therefore there is a need for a method of arbitrating speakerphone operation in a portable communication device that eliminates falsing due to echoes.